Real Project Reviews: Choosing Materials for Milling Machine Parts

milling machine parts-feature image

A lot of plastic prototypes are milling machine parts, regular plastics like ABS, PC, PMMA, POM, and PEEK block material can be machined by CNC milling machines or CNC turning machines. Explore more details on how to make CNC machined parts here.

If you want to have a prototype made, and you have a specific material requirement for example clear PC. Then the process is limited to CNC-machining (CNC milling or turning). Of course, injection molding probably could also produce this part. However, it is unrealistic to spend thousands or millions of dollars making one prototype.

In this article, I’m going to write two real stories regarding plastic material choice, inspired by real projects. (Name, company, and product will be anonymous for confidentiality reasons).

1. Keeping the Color Consistent With Different Plastic Milling Machine Parts

An old customer came to us with a new inquiry for a new prototype. The material requested for three of the parts is white PA6 (Nylon).  Two of the parts need to be glued together and polished.

However, as it might be known to some people, the Nylon material is “self-lubricated”, thus cannot be glued with other parts. And Nylon material is not recommended to be polished, due to the material properties of the material itself, after polishing the surface of milled Nylon part would become even rougher than the parts only milled by CNC machines.

The customer then changed two parts that need gluing to white PC, which can be glued (though the PC parts can’t be glued strongly) and polished quite smooth.

However, as this customer cares a lot about the aesthetics of this prototype if all the parts need to be assembled and presented to important clients, the color of the parts must be consistent. The thing is even if the PC and Nylon materials are all white, they are slightly different white. The following photos were taken by me to show our customer the difference:

White PC, white Nylon (PA66), white Nylon (PA6)

As it is shown above in the photos, although they are all white colors, they are a little different in reality. It is a small detail, but if aesthetics are really important for a prototype, for example, the prototypes are to be presented to important customers or on an exhibition, then it is not a good idea to ignore the consistency of the colors of different materials.

Back to the story, upon seeing the photos, the customer chose white ABS for all three parts and was quite satisfied with how the whole part turned out in the end.

White PC, white Nylon (PA66), white Nylon (PA6)


2. Is There An Alternative for Clear PC Milling Machine Parts?

As I have stated in the beginning, if the material has to be PC, then the only process for making a prototype is CNC machining. But what if I only need the prototype to be clear, it can be any clear material and I want the cost to be as low as possible?

A new customer sent us a few design files with a simple message: “This needs to be a clear polished polycarbonate prototype. There is a part that needs to be clear Teflon” (Information partly concealed for confidentiality reasons).

Because the message was quite simple, and there is no clear Teflon block material (only Teflon clear pellets used for injection molding), I called the cell phone number left by the customer.

After communications, I learned that the whole part needs to hold about 5 gallons of water and the material doesn’t have to be PC. All the parts can be other clear materials. The customer would like to spend as little money as possible to make the prototype and test if the whole item functions as it’s supposed to.  The part doesn’t have to be very clear. It’s acceptable if one can see inside the part. If it’s too expensive to make the clear part, then if the part is not that clear it’s okay.

Machined PC without any finish

After I got all this information, I recommended using 3D printing to make this part and clear-polish for the surface finish. For 3D-printing can make a lot of complex shapes and usually costs a lot less compared to CNC-machining. Sometimes if a part is too complex for the CNC milling machines, the part has to be split into several parts, machined separately, and glued in the end.

Machined PC with only vapor-polish

In this case, considering the part needs to hold quite a lot of water, it would be best if we don’t split the parts, because no matter how strong the glue is, there is a possibility that the glued parts couldn’t hold that much amount of water.

For 3D-printing, the disadvantages are that there might small clear bubbles inside the printed parts, the material is quite limited, for SLA, the only material available is photosensitive resin, and for SLS, the finished parts have a quite rough surface, which can neither be polished nor painted to have better aesthetics.

Machined PC with vapor-polish and manual polish

After a preliminary review of the designs by my engineering team and me, we offered five machining proposals for the customer: CNC milling PC with vapor-polish, CNC milling PC without vapor polish, 3D-printing with clear polish, 3D-printing without polish, and 3D printing with just one part polished. Also, a few sample photos were sent to the customer to see what each part would look like in the end.

In this particular case, if the material has to be polycarbonate, some parts would need splitting and gluing, due to the structure of the design and limitations of CNC machining itself. We provided a very specific splitting and gluing plan (the part needs to hold about 5 gallons of water considered) to the customer. Also, the surface of the milling machine polycarbonate parts are quite foggy, not clear, therefore to make the part clear, we have to use vapor polish. If the clearness requirement is high, then the part has to be vapor-polished and manually polished. In this case, we only quoted vapor-polish for the surface finish.

If using 3D-printing (SLA), then we don’t need to split the parts, they all can be machined as whole pieces then assemble. But the parts that have just been printed, even it is clear material, the part itself is foggy, and we have to polish it by hand to make it clear.

Among the five proposals, the highest cost is CNC milling PC with vapor polish, while the lowest is 3D-printing (SLA) clear material without polish.

After seeing all of our proposals, the customer decided to go with 3D printing and polishing one part that has to be clear. The part functions quite well and the part now is ready for injection molding.

In conclusion

Although in the above projects, choosing the suitable plastic materials are small details, we are always patient and committed to providing the optimal services for our customers.

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